Low temperature sintered ceramic material for use in solid dielectric capacitors or the like, and method of manufacture

ABSTRACT

A ceramic composition capable of sintering at a sufficiently low temperature to enable the use of a low cost base metal as the electrode material in the fabrication of capacitors. The major ingredient of the composition is expressed as Ba k-x-y  M x  L y  O k  TiO 2 , where M is at least either of magnesium and zinc, L is at least either of strontium and calcium, k, x and y are numerals in the ranges of 1.00 to 1.04, 0.002 to 0.049, and 0.001 to 0.048, respectively, and x+y is a value in the range of 0.02 to 0.05. To this major ingredient is added a minor proportion of a mixture of lithium oxide, silicon dioxide, and, possibly, at least one of barium oxide, calcium oxide, and strontium oxide. For the fabrication of coherently bonded bodies of this composition, as for use as the dielectric bodies of capacitors, the moldings of the mixture of the major ingredient and additive in finely divided form are sintered in a reductive or neutral atmosphere and then reheated at a lower temperature in an oxidative atmosphere. The sintering temperature can be so low (typically from 1050°  to 1200° C.) that the moldings can be co-sintered with base metal electrodes buried therein without difficulties encountered heretofore.

BACKGROUND OF THE INVENTION

Our invention relates to dielectric ceramic compositions that allowsintering or firing at lower temperatures than heretofore, and to aprocess for the fabrication of coherently bonded bodies of suchcompositions. The low temperature sintered ceramic materials of ourinvention find a typical application in solid dielectric capacitors,particularly in those of the monolithic or multilayered design, makingpossible the use of a base metal as the material for the film electrodesof such capacitors.

Multilayered ceramic capacitors are known which employ noble metals suchas platinum and palladium as the electrode materials. For themanufacture of such multilayered capacitors, as heretofore practiced,there are first prepared green dielectric sheets from the proportionedingredients for a dielectric ceramic material in finely divided form. Anelectroconductive paste containing powdered platinum or palladium isthen "printed" on the green sheets in a desired pattern. Several suchprinted green sheets are stacked up, pressed together, and sintered inan temperature range of 1300° to 1600° C. in an oxidative atmosphere.This conventional method makes possible the simultaneous production(co-sintering) of the dielectric ceramic bodies and the film electrodesinterleaved therein. It is also an acknowledged advantage of the knownmethod that the noble metal electrodes are totally unaffected by thehigh temperature sintering in an oxidative atmosphere. Offsetting allthese advantages is the expensiveness of the noble metals, which addsconsiderably to the costs of the multilayered ceramic capacitors.

A solution to this problem is found in Sakabe et al. U.S. Pat. No.4,115,493 issued Sept. 19, 1978. This patent proposes a method of makinga monolithic ceramic capacitor with use of a base metal such as nickel,iron or cobalt, or an alloy thereof, as the electrode material.According to this prior art method, a paste of a powdered base metal isscreened on green dielectric sheets, and the pasted sheets are stacked,pressed together, and fired in a temperature range of 1300° to 1370° C.in a reductive atmosphere containing hydrogen. The oxidation of thepasted base metal particles is thus avoided.

We do, however, object to the Sakabe et al. method for the followingreasons. We have discovered from experiment that the firing temperaturerange of 1300° to 1370° C. suggested by this prior art method leads toeasy flocculation of the particles of nickel or like base metal pastedon the green dielectric sheets. The base metal particles have also beenfound to tend to diffuse into the ceramic bodies when fired in thattemperature range. The flocculation and diffusion of the base metalparticles are, of course, both undesirable as the resulting capacitorswill not possess desired values of capacitance and insulationresistance.

SUMMARY OF THE INVENTION

Our invention provides a solution to the problem of how to reduce thesintering temperature of ceramic compositions, particularly in themanufacture of solid dielectric capacitors, to make possible the use ofa low cost base metal as the electrode material without the noteddifficulties encountered heretofore. The low temperature sinteredceramic compositions in accordance with our invention are also wellcalculated for the provision of capacitors of very favorable performancecharacteristics.

Stated in brief, a low temperature sintered ceramic material inaccordance with our invention consists essentially of 100 parts byweight of a major ingredient expressed by the formula Ba_(k-x-y) M_(x)L_(y) O_(k) TiO₂, and 0.2 to 10.0 parts by weight of an additive mixtureof lithium oxide (Li₂ O) and silicon dioxide (SiO₂). In the formula ofthe major ingredient, M is at least either of magnesium (Mg) and zinc(Zn); L is at least either of strontium (Sr) and calcium (Ca); k is anumeral in the range of 1.00 to 1.04; x is a numeral in the range of0.002 to 0.049; y is a numeral in the range of 0.001 to 0.048; and k+yis a value in the range of 0.02 to 0.05. The additive mixture may, ormay not, additionally comprise at least one metal oxide (MO) selectedfrom the group consisting of barium oxide (BaO), calcium oxide (CaO),and strontium oxide (SrO).

According to the method of our invention, for the fabrication ofcoherently bonded bodies of the above low temperature sintered ceramicmaterial, there are first prepared the major ingredient, Ba_(k-x-y)M_(x) L_(y) O_(k) TiO₂, and the additive mixture of Li₂ O and SiO₂, withor without MO, in the above suggested proportions. After having beenintimately mixed together, the major ingredient and additive are moldedinto bodies of desired shape and size. The moldings are subsequentlysintered in a nonoxidative (i.e. neutral or reductive) atmosphere andthen reheated in an oxidative atmosphere.

The dielectric ceramic composition of our invention, set forth in theforegoing, makes it possible to sinter the moldings in an nonoxidativeatmosphere at temperatures less than 1200° C. A temperature range forthis sintering operation is from 1050° C. to 1200° C. for the bestresults. The sintering temperatures of less than 1200° C. enable theuse, in the fabrication of capacitors with the ceramic composition ofour invention as the dielectric, of nickel or like low cost base metalas the electrode material without the difficulties that have beenpointed out in connection with the prior art. The sintering temperaturemight be above 1200° C. Should it exceed 1300° C., however, the basemetal particles pasted on dielectric bodies might flocculate or diffuse.Should the temperature be too low, on the other hand, then thedielectric bodies might not be sintered to maturity. Hence the preferredtemperature range of 1050° to 1200° C. We recommend this temperaturerange not only because the base metal electrodes can be formed favorablybut also because it realizes a substantial curtailment of the energythat has heretofore been consumed for firing the dielectric moldings.

The reheating of the sintered bodies in an oxidative atmosphere inaccordance with the method of our invention is intended to compensatefor the oxygen vacancies in the bodies that have been caused by theprevious firing in a nonoxidative atmosphere and hence to increase theirinsulation resistance to a required degree. Thus the sintered bodies maybe reheated at temperatures ranging from 500° C. to 1000° C. Thereheating temperature should be lower than the preceding sinteringtemperature.

We also recommend that the periods of time for the sintering in anonoxidative atmosphere and for the reheating in an oxidative atmospherebe minimums required for the accomplishment of the purposes for whichthe treatments are intended respectively. Experiment has proved that themoldings should be sintered at the maximum temperature for two to fourhours, and subsequently reheated for 10 to 60 minutes, for the bestresults.

In addition to the advantages already set forth, our invention makespossible the provision of capacitors having specific dielectricconstants of over 2000, dielectric losses of less than 2.5 percent,resistivity of over 1×10⁶ megohm-centimeters, and temperaturedependences of capacitances of plus or minus 10 percent in a temperaturerange of -25° to +85° C.

The above and other features and advantages of our invention and themanner of realizing them will become more apparent, and the inventionitself will best be understood, from a study of the following detaileddescription and appended claims, with reference had to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional representation of an experimental multilayeredceramic capacitor employing the low temperature sintered ceramicmaterial of our invention, the capacitor being representative ofnumerous test capacitors fabricated in the Examples of the invention setforth subsequently;

FIG. 2 is a graph plotting the average capacitance-temperaturecharacteristic of test capacitors, each consturcted as in FIG. 1,manufactured in Test No. 1 in Example I of our invention;

FIG. 3 is a graph plotting the average capacitance-temperaturecharacteristic of test capacitors, each constructed as in FIG. 1,manufactured in Test No. 29 in Example II of our invention; and

FIG. 4 is a ternary diagram depicting the proportions of Li₂ O, SiO₂,and MO (at least one of BaO, CaO and SrO) which can be employed incombination as an additive mixture in the ceramic compositions inaccordance with our invention.

DETAILED DESCRIPTION

We have illustrated in FIG. 1 one of many similar multilayered ceramiccapacitor fabricated in various Examples of our invention by way of apossible application of our invention, each capacitor having itsdielectric body formulated in accordance with the composition and methodof our invention. Generally designated by the reference numeral 10, therepresentative capacitor is shown to have an alternating arrangement ofthree dielectric ceramic layers 12 and two film electrodes 14. Thedielectric layers 12 have, of course, the low temperature sinteredceramic material of our invention. The film electrodes 14, which can beof a low cost base metal such as nickel, extend into the middle of thedielectric body 15, composed of the three dielectric layers 12, from theopposite sides thereof into a partly opposed relation with each other. Apair of conductive terminations 16 contact the respective filmelectrodes 14. Each termination 16 comprises a baked on zinc layer 18, aplated on copper layer 20, and a plated on solder layer 22.

Typically, and as fabricated in the subsequent Examples of ourinvention, the intermediate one of the three dielectric layers 12 has athickness of 0.02 millimeters. The area of that part of each filmelectrode 14 which is opposed to the other film electrode is 25 squaremillimeters (5×5 millimeters).

EXAMPLE I

In this Example, we fabricated 28 different sets of multilayered ceramiccapacitors, each constructed as in FIG. 1, having their dielectricbodies 15 formulated in accordance with the compositions set forth inTable 1. The major ingredient of the ceramic compositions in accordancewith our invention has been expressed as Ba_(k-x-y) M_(x) L_(y) O_(k)TiO₂, where M is at least either of Mg and Zn and where L is at leasteither of Sr and Ca. Accordingly, in Table 1, we have given the specificatomic numbers, as represented by k-x-y,x, y and k, of the elements Ba,M (Mg and/or Zn), L (Sr and/or Ca) and O of the major ingredient, aswell as the total atomic numbers of Mg and Zn and the total atomicnumbers of Sr and Ca. We employed a mixture of only Li₂ O and SiO₂ as anadditive in this Example. Table 1 specifies the amounts, in parts byweight, of this additive with respect to 100 parts by weight of themajor ingredient, and the relative proportions, in mole percent, of Li₂O and SiO₂.

                                      TABLE 1                                     __________________________________________________________________________    Ceramic Compositions                                                          Major Ingredient (100 wt. pt.)   Additive                                     Test  x           y              Propn.                                                                             Comp. (mole %)                          No.                                                                              k-x-y                                                                            Mg  Zn  Total                                                                             Sr  Ca  Total                                                                             k  (wt. pt.)                                                                          Li.sub.2 O                                                                         SiO.sub.2                          __________________________________________________________________________     1 1.02                                                                              0.005                                                                             0.005                                                                            0.01                                                                               0.005                                                                             0.005                                                                            0.01                                                                              1.04                                                                             1.0  27   73                                  2 1.02                                                                              0.005                                                                            --   0.005                                                                             0.005                                                                            --   0.005                                                                            1.03                                                                             7.0  40   60                                  3 1.02                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.01                                                                              --  0.01                                                                              1.05                                                                             5.0  40   60                                  4 1.01                                                                             --   0.005                                                                             0.005                                                                            --   0.005                                                                             0.005                                                                            1.02                                                                             1.0  40   60                                  5 1.01                                                                             --  0.01                                                                              0.01                                                                               0.005                                                                             0.005                                                                            0.01                                                                              1.03                                                                             12.0 40   60                                  6 1.01                                                                              0.005                                                                            --   0.005                                                                            --   0.025                                                                             0.025                                                                            1.04                                                                             1.0  40   60                                  7 1.00                                                                             --  0.01                                                                              0.01                                                                              --  0.01                                                                              0.01                                                                              1.02                                                                             0.2  48   52                                  8 1.00                                                                             --  0.01                                                                              0.01                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.03                                                                             3.0  40   60                                  9 1.00                                                                             --  0.01                                                                              0.01                                                                              --  0.03                                                                              0.03                                                                              1.04                                                                             1.0  40   60                                 10 0.99                                                                             0.01                                                                              0.01                                                                              0.02                                                                              --  0.02                                                                              0.02                                                                              1.03                                                                             3.0  55   45                                 11 0.99                                                                             --   0.002                                                                             0.002                                                                            --   0.048                                                                             0.048                                                                            1.04                                                                             10.0 50   50                                 12 0.99                                                                              0.049                                                                            --  0.049                                                                             --   0.001                                                                             0.001                                                                            1.04                                                                             0.2  25   75                                 13 0.98                                                                             0.01                                                                              --  0.01                                                                              0.01                                                                              --  0.01                                                                              1.0                                                                              10.0 50   50                                 14 0.98                                                                             --   0.005                                                                             0.005                                                                             0.025                                                                            --   0.025                                                                            1.01                                                                             0.2  27   73                                 15 0.98                                                                             --  0.03                                                                              0.03                                                                              --  0.01                                                                              0.01                                                                              1.02                                                                             0.2  40   60                                 16 0.98                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.02                                                                             3.0  33   67                                 17 0.98                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.02                                                                              --  0.02                                                                              1.02                                                                             0.0  --   --                                 18 0.98                                                                             --  0.02                                                                              0.02                                                                              0.02                                                                              0.01                                                                              0.03                                                                              1.03                                                                             1.0  27   73                                 19 0.97                                                                             0.01                                                                              --  0.01                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.00                                                                             1.0  48   52                                 20 0.97                                                                             0.01                                                                              --  0.01                                                                              0.03                                                                              --  0.03                                                                              1.01                                                                             5.0  33   67                                 21 0.97                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.02                                                                              0.01                                                                              0.03                                                                              1.02                                                                             5.0  20   80                                 22 0.97                                                                             0.02                                                                              0.02                                                                              0.04                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.03                                                                             0.2  33   67                                 23 0.96                                                                             0.03                                                                              --  0.03                                                                              0.01                                                                              --  0.01                                                                              1.00                                                                             1.0  25   75                                 24 0.96                                                                             0.02                                                                              --  0.02                                                                              0.01                                                                              0.02                                                                              0.03                                                                              1.01                                                                             1.0  33   67                                 25 0.95                                                                              0.002                                                                            --  0.02                                                                               0.048                                                                            --   0.048                                                                            1.00                                                                             0.2  25   75                                 26 0.95                                                                             --   0.049                                                                             0.049                                                                             0.001                                                                            --   0.001                                                                            1.0                                                                              10.0 50   50                                 27 0.93                                                                             0.02                                                                              --  0.02                                                                              0.03                                                                              --  0.03                                                                              0.98                                                                             7.0  40   60                                 28  0.989                                                                            0.001                                                                            --   0.001                                                                            --  0.02                                                                              0.02                                                                              1.00                                                                             1.0  50   50                                 __________________________________________________________________________

Thus, according to Test No. 1 of Table 1, for instance, the majoringredient was Ba₁.02 M₀.01 L₀.01 O₁.04 TiO₂ or, more exactly, Ba₁.02Mg₀.005 Zn₀.005 Sr₀.005 O₁.04 TiO₂. One hundred parts by weight of thismajor ingredient was admixed with 1.0 parts by weight of a mixture of 27mole percent Li₂ O and 73 mole percent SiO₂.

For the fabrication of test capacitors of the Test No. 1 composition, westarted with the preparation of the major ingredient, Ba₁.02 Mg₀.005Zn₀.005 Sr₀.005 O₁.04 TiO₂. We first prepared 926.39 grams of BaCO₃,0.94 grams of MgO, 1.88 grams of ZnO, 3.40 grams of SrCO₃, 2.32 grams ofCaCO₃, and 368.44 grams of TiO₂, all with purities of over 99.0 percent.Expressed in mole parts, the relative proportions of the above preparedBaCO₃, MgO, ZnO, SrO, CaO, and TiO₂ were 1.02, 0.005, 0.005, 0.005,0.005, and 1.0, respectively, aside from the impurities contained in thestart materials. These start materials were wet mixed together for 15hours. Then the mixture was dried at 150° C. for four hours, pulverized,and calcined in air at about 1200° C. for two hours. The majoringredient was thus obtained in finely divided form.

We prepared the additive of Test No. 1 by first preparing a mixture of31.26 grams (27 mole percent) of Li₂ CO₃ and 68.74 grams (73 molepercent) of SiO₂. To this mixture was added 300 cubic centmeters ofalcohol, and the resulting mixture was agitated for 10 hours in apolyethylene pot with alumina balls. Then the mixture was air fired at1000° C. for two hours. Then, charged into an alumina pot together with300 cubic centimeters of water, the mixture was crushed with aluminaballs for 15 hours. Then the crushed mixture was dried at 150° C. forfour hours. There was thus obtained the desired additive mixture of 27mole percent Li₂ O and 73 mole percent SiO₂ in finely divided form.

Then 1000 grams of the above prepared major ingredient and 10 grams (oneweight percent) of the above prepared additive was mixed together.Further, to this mixture, we added 15 percent by weight of an organicbinder and 50 percent by weight of water with respect to the totalamount of the major ingredient and the additive. The organic binder wasan aqueous solution of acrylic ester polymer, glycerine, and condensedphosphate. All these were ball milled into a slurry. Then this slurrywas defoamed in vacuum. Then the deformed slurry was introduced into areverse roll coater thereby to be shaped into a thin, continuous stripon an elongate strip of polyester film. Then the continuous strip of theslurry was dried at 100° C. on the polyester film. The green(unsintered) ceramic strip thus obtained, about 25 microns thick, wassubsequently cut into "squares" sized 10 by 10 centimeters.

For the fabrication of the base metal film electrodes 14, we prepared 10grams of nickel in finely divided form, with an average particle size of1.5 microns, and a solution of 0.9 gram of ethyl cellulose in 9.1 gramsof butyl "Carbitol" (trademark for diethylene glycol monobutyl ether).Both were agitated for 10 hours to provide an electroconductive paste.Then this paste was "printed" on one surface of each green ceramicsheet, which had been prepared as above, through a screen havingapproximately 50 rectangular perforations sized 7 by 14 millimeters.Then, after drying the printed paste, two green ceramic sheets werestacked, with their printings directed upwardly, and with the printingson the two sheets offset from each other to an extent approximately onehalf of their longitudinal dimension. Further, four green ceramic sheetseach with a thickness of 60 microns were stacked on each of the top andbottom surfaces of the two printed ceramic sheets. Then the stackedsheets were pressed in their thickness direction under a pressure ofapproximately 40 tons at 50° C., thereby bonding the stacked sheets toone another. Then the bonded sheets were cut in a latticed pattern intoapproximately 100 pieces.

We employed a furnace capable of atmosphere control for co-firing theabove prepared green dielectric bodies and what were to become filmelectrodes buried therein. The bodies were first air heated to 600° C.at a rate of 100° C. per hour, thereby driving off the organic binderthat had been used for providing the slurry of the powdered majoringredient and additive. Then, with the furnace atmosphere changed fromair to a reductive (nonoxidative) atmosphere consisting of two percentby volume of molecular hydrogen and 98 percent by volume of molecularnitrogen, the furnace temperature was raised from 600° C. to 1160° C. ata rate of 100° C. per hour. The maximum temperature of 1160° C., atwhich the ceramic bodies could be sintered to maturity, was maintainedfor three hours. Then the furnace temperature was lowered to 600° C. ata rate of 100° C. per hour. Then the furnace atmosphere was againchanged to air (oxidative atmosphere), and the temperature of 600° C.was maintained for 30 minutes in that atmosphere for the oxidative heattreatment of the sintered bodies. Then the furnace temperature wasallowed to lower to room temperature. There were thus obtained thedielectric ceramic bodies 15, FIG. 1, co-sintered with the filmelectrodes 14 buried therein.

We proceeded to the production of the pair of conductive terminations 16on both sides of each ceramic body 15. First, for the fabrication of theinmost zinc layers 18, an electroconductive paste composed of zinc,glass frit, and vehicle was coated on both sides of each ceramic body15. The coatings were dried and air heated at 550° C. for 15 minutes,thereby completing the zinc layers 18, each in direct contact with oneof the two film electrodes 14 buried in each ceramic body 15. Then theintermediate copper layers 20 were formed on the zinc layers 18 byelectroless plating. The outermost solder layers 22 were formedsubsequently by electroplating a lead-tin alloy onto the copper layers20.

There were thus completed the fabrication of multilayered ceramiccapacitors, each constructed as in FIG. 1, of Test No. 1. Thecomposition of the sintered ceramic bodies 10 is substantially the sameas that before sintering. Essentially, therefore, it is reasoned thatthe ceramic bodies 15 are of perovskite structures, with the additive(mixture of 27 mole percent Li₂ O and 73 mole percent SiO₂)substantially uniformly dispersed among the crystal grains of the majoringredient (Ba₁.02 Mg₀.005 Zn₀.005 Sr₀.005 Ca₀.005 O₁.04 TiO₂).

We have so far described the method of fabricating multilayered ceramiccapacitors in accordance with the composition of Test No. 1. As regardsthe other ceramic compositions of Table I, designated Tests Nos. 2through 28, we manufactured similar multilayered ceramic capacitorsthrough exactly the same procedure as that of Test No. 1 except forchanges in the temperature of firing (sintering) in the reductive(nonoxidative) atmosphere.

The multilayered ceramic capacitors of Test Nos. 1 through 28 were thentested as to their specific dielectric constants, dielectric losses,resistivities, and percent changes in capacitances from those at +20° C.to those at -25° C. and +85° C. We measured these electrical propertiesof the test capacitors as follows:

1. Specific Dielectric Constant

The capacitance of each test capacitor was first measured at atemperature of 20° C., a frequency of one kilohertz, and an effectivevoltage of 0.5 volt. Then the specific dielectric constant was computedfrom the measured value of capacitance, and the area (25 squaremillimeters) of each of the opposed parts of the film electrodes 14, andthe thickness (0.02 millimeter) of that ceramic layer 12 whichintervenes between the film electrodes.

2. Dielectric Loss

Under the same conditions as the specific dielectric constant.

3. Resistivity

Resistance between the pair of terminations 16 of each test capacitorwas measured after the application of a direct current at 50 volts forone minute. Then resistivity was computed from the measured resistancevalue and size of each test capacitor.

4. Capacitance-Temperature Characteristic

The test capacitors were introduced into a thermostatic oven, and attemperatures of -25°, 0°, +20°, +40°, +60°, and +85° C., theircapacitances were measured at a frequency of one kilohertz and aneffective voltage of 0.5 volt. Then the percent changes of thecapacitances from those at 20° C. to the other specified temperatureswere ascertained.

Table 2 gives the results of the measurements by the above methods. Itwill be seen from this table that the specific dielectric constants ofthe Test No. 1 capacitors, for instance, averaged 3060, their dielectriclosses 1.5 percent, their resistivities 2.8×10⁶ megohm-centimeters, andtheir percent variations of capacitances from those at +20° C. to thoseat -25° and +85° C., -9.1 and +6.5 percent, respectively.

FIG. 2 graphically represents the average percent variations of thecapacitances of the Test No. 1 capacitors at the above specifiedtemperatures with respect to their capacitances at +20° C. It will benoted that the capacitance variations in the temperature range of -25°to -85° C. are all in the range of plus or minus 10 percent. Thiscapacitance-temperature characteristic was typical of all the testcapacitors of Example I; that is, if the percent variations of thecapacitances of any groups of test capacitors at -25° and +85° C. werewithin plus or minus 10 percent, so were their capacitance variations atthe other temperatures in between.

                                      TABLE 2                                     __________________________________________________________________________    Firing Temperatures & Capacitor Characteristics                                      Capacitor Characteristics                                                 Firing                                                                            Specific                                                                            Dielectric                                                       Test                                                                             Temp.                                                                             Dielectric                                                                          Loss  Resistivity                                                                          Capacitance Variations (%)                          No.                                                                              (°C.)                                                                      Constant                                                                            (%)   (megohm-cm)                                                                          At -25° C.                                                                    At +85° C.                            __________________________________________________________________________     1 1160                                                                              3060  1.5   2.8 × 10.sup.6                                                                 -9.1   +6.5                                          2 1070                                                                              2860  1.8   3.2 × 10.sup.6                                                                 -12.4  +11.1                                         3 1250                                                                              Not coherently bonded on firing.                                        4 1150                                                                              3030  1.6   2.9 × 10.sup.6                                                                 -12.2  +16.5                                         5 1070                                                                              2780  3.5   3.2 × 10.sup.5                                                                 -7.4   +2.6                                          6 1150                                                                              3140  1.7   2.4 × 10.sup.6                                                                 -7.2   +1.8                                          7 1170                                                                              3220  1.9   1.8 × 10.sup.6                                                                 -9.1   +5.2                                          8 1120                                                                              3030  1.4   5.3 × 10.sup.6                                                                 -8.5   +6.4                                          9 1150                                                                              3070  1.5   2.6 × 10.sup.6                                                                 -7.1   -2.4                                         10 1110                                                                              2910  3.1   7.5 × 10.sup.5                                                                 -7.4   -3.8                                         11 1070                                                                              2760  2.4   1.1 × 10.sup.6                                                                 -9.5   -6.8                                         12 1190                                                                              2870  1.7   2.1 × 10.sup.6                                                                 -9.0   -9.2                                         13 1070                                                                              2810  2.3   1.5 × 10.sup.6                                                                 -7.2   -1.5                                         14 1190                                                                              3230  1.8   1.6 × 10.sup.6                                                                 -6.5   +4.8                                         15 1180                                                                              3120  1.9   1.4 × 10.sup.6                                                                 -7.2   -4.3                                         16 1120                                                                              2900  1.3   5.8 × 10.sup.6                                                                 -7.4   -2.3                                         17 1250                                                                              Not coherently bonded on firing.                                       18 1160                                                                              2890  1.3   3.8 × 10.sup.6                                                                 -8.8   -2.5                                         19 1140                                                                              3110  1.8   3.5 × 10.sup.6                                                                 -6.3   +1.4                                         20 1100                                                                              2970  1.5   5.8 × 10.sup.6                                                                 -8.2   -0.6                                         21 1250                                                                              Not coherently bonded on firing.                                       22 1180                                                                              2830  1.7   3.5 × 10.sup.6                                                                 -13.5  -8.5                                         23 1160                                                                              2920  1.5   3.7 × 10.sup.6                                                                 -7.8   -6.4                                         24 1150                                                                              2860  1.6   3.3 × 10.sup.6                                                                 -7.2   -3.2                                         25 1190                                                                              3030  1.6   3.5 × 10.sup.6                                                                 -9.2   +0.5                                         26 1070                                                                              2640  2.3   1.5 × 10.sup.6                                                                 -9.1   -8.3                                         27 1070                                                                              2680  8.4   2.8 × 10.sup.3                                                                 -8.3   -4.5                                         28 1140                                                                              3080  2.8   1.2 × 10.sup.6                                                                 -8.6   +7.5                                         __________________________________________________________________________

Before proceeding further with the examination of Table 2, we willdetermine the acceptable criteria of the four electrical characteristicsin question of capacitors in general as follows:

Specific dielectric constant, at least 2000.

Dielectric loss, not more than 2.5 percent.

Resistivity, at least 1×10⁶ megohm-centimeters.

Temperature dependence of capacitance, within plus or minus 10 percent.

A reconsideration of Table 2 in light of the above established criteriaof favorable capacitor characteristics will reveal that the capacitorsof Test Nos. 2, 3, 4, 5, 10, 17, 21, 22, 27 and 28 do not meet thesecriteria. Accordingly, the corresponding ceramic compositions of Table 1fall outside the scope of our invention.

Now, let us study the ceramic compositions of Table 1 and thecorresponding capacitor characteristics of Table 2 in more detail. Theceramic composition of Test No. 17 contained no additives specified byour invention. The dielectric bodies formulated accordingly were notcoherently bonded on firing at a temperature as high as 1250° C.Consider the ceramic composition of Test No. 7 for comparison. Itcontained 0.2 part by weight of the additive with respect to 100 partsby weight of the major ingredient. Even though the firing temperaturewas as low as 1170° C., the Test No. 9 capacitors possess the desiredelectrical characteristics. We set, therefore, the lower limit of thepossible proportions of the additive at 0.2 part by weight with respectto 100 parts by weight of the major ingredient.

The Test No. 5 ceramic composition contained as much as 12 parts byweight of the additive with respect to 100 parts by weight of the majoringredient. The resulting capacitors have an average dielectric loss of3.5 percent, which is higher than the above established criterion.However, when the proportion of the additive was reduced to 10 parts byweight, as in the Test No. 11 ceramic composition, then the resultingcapacitors have the desired electrical characteristics. Accordingly, theupper limit of the possible proportions of the additive is set at 10parts by weight with respect to 100 parts by weight of the majoringredient.

As for the major ingredient, Ba_(k-x-y) M_(x) L_(y) O_(k) TiO₂, thevalue of x+y was set at 0.01 in Test No. 2. In the resulting capacitors,the average variations of capacitances at -25° and +85° C. are -12.4 and+11.1 percent, both outside the desired range of plus or minus 10percent. However, when the value of x+y was increased to 0.02, as inTest No. 1, then the desired electrical characteristics could all beobtained. Thus the lowermost possible value of x+y is 0.02. The Test No.22 composition had the value of x+y set at as high as 0.06. In theresulting capacitors, the average variation of capacitance at -25° C. is-13.5 percent, which also is outside the desired range of plus or minus10 percent. In Test No. 18, the value of x+y was set slightly lower, at0.05, and the resulting capacitors possess all the desired electricalcharacteristics. The uppermost possible value of x+y is therefore 0.05.

The value of x was set at 0.001 in Test No. 28. The resulting capacitorhas an average dielectric loss of 2.8 percent, which exceeds the desiredlimit of not more than 2.5 percent. The value of x was set at 0.002 inTests Nos. 11 and 25, and the resulting capacitors had the desiredelectrical characteristics. The lowermost possible value of x istherefore 0.002.

Sr and Ca, represented by the capital L in the formula of the majoringredient, both function to expedite the sintering of the ceramicbodies formulated in accordance with our invention. As will be seen fromTests Nos. 12 and 26, Sr and Ca both perform their intended functionwhen the value of y in the formula of the major ingredient is at least0.001. The lowermost possible value of y is therefore 0.001.

Since we have set the maximum possible value of x+y at 0.05, and theminimum possible value of y at 0.001, it follows that the maximumpossible value of x is 0.049. Further, since we have set the minimumpossible value of x at 0.002, the maximum possible value of y must be0.048. As will be seen from the results of Table 2, x can be in therange of 0.002 to 0.049, y in the range of 0.001 to 0.048, and x+y inthe range of 0.02 to 0.05, regardless of whether either or both of Mgand Zn are employed as M, and whether either or both of Sr and Ca areemployed as L.

The value of k in the formula of the major ingredient was set at 0.98 inTest No. 27, with the result that the average resistivity of theassociated capacitors is 2.8×10³ megohm-centimeters, much lower than therequired minimum. However, the desired criteria of resistivity and otherproperties were obtained when k was set at 1.00 as in Tests Nos. 25 and26. The lowermost possible value of k is therefore 1.00. On the otherhand, when the value of k was increased to 1.05, as in Test No. 3, theresulting dielectric bodies were not coherently bonded on firing. As inTest No. 1, however, the desired electrical characteristics resultedwhen the value of k was set at 1.04. Accordingly, the uppermost possiblevalue of k is 1.04.

Concerning the composition of the additive, the mixture of Li₂ O andSiO₂ in this Example, it will be noted from Test No. 10 that when theproportion of SiO₂ with respect to that of Li₂ O was set at 45 molepercent, the average dielectric loss of the resulting capacitors is 3.1percent, much higher than the desired value of 2.5 percent. The desiredelectrical characteristics were all obtained, however, when the SiO₂proportion was set at 50 mole percent as in Test No. 11. On the otherhand, when the SiO₂ proportion was increased to 80 mole percent as inTest No. 21, the dielectric bodies of the resulting composition were notcoherently bonded on firing. The desired electrical characteristics wereall obtained when the SiO₂ proportion was up to only 75 mole percent asin Test No. 25. We conclude from these findings that the acceptablerange of the proportions of SiO₂ is from 50 to 75 mole percent and,consequently, that the acceptable range of the proportions of Li₂ O isfrom 25 to 50 mole percent.

EXAMPLE II

In this Example, we added MO (at least one of BaO, CaO, and SrO) to theadditive which in the preceding Example, was a mixture of only Li₂ O andSiO₂. We prepared various ceramic compositions set forth as Tests Nos.29 through 72 in Table 3. As will be seen from this Table, the atomicnumbers k-x-y, x, y and k of the major ingredient, Ba_(k-x-y) M_(x)L_(y) O_(k) TiO₂, were determined variously. The relative proportions ofthe ingredients, Li₂ O, SiO₂, and MO, of the additive were alsodetermined variously and are given in mole percent in Table 3. As theMO, we employed one, two, or all of BaO, CaO, and SrO. In cases wheretwo or three of these compounds were employed in combination, theirrelative proportions were also determined variously and are expressed inmole percent in Table 3. Thus, in Test No. 29, for instance, theadditive in use was a mixture of five mole percent Li₂ O, 70 molepercent SiO.sub. 2, 15 mole percent BaO, 8.75 mole percent CaO, and 1.25mole percent SrO. The proportions of the additives are given in parts byweight with respect to 100 parts by weight of the major ingredient.

                                      TABLE 3                                     __________________________________________________________________________    Ceramic Compositions                                                          Major Ingredient (100 wt. pt.)   Additive                                     Test  x           y              Propn.                                                                             Comp. (mole %)                                                                         MO (mole %)                    No.                                                                              k-x-y                                                                            Mg  Zn  Total                                                                             Sr  Ca  Total                                                                             k  (wt. pt.)                                                                          Li.sub.2 O                                                                       SiO.sub.2                                                                        MO BaO                                                                              CaO                                                                              SrO                      __________________________________________________________________________    29 1.02                                                                              0.005                                                                             0.005                                                                            0.01                                                                              0.01                                                                              --  0.01                                                                              1.04                                                                             10.0  5 70 25 60 35  5                       30 1.03                                                                              0.005                                                                            --   0.005                                                                             0.005                                                                            0.01                                                                               0.015                                                                            1.05                                                                             3.0  15 55 30 90  5  5                       31 1.02                                                                             --   0.005                                                                             0.005                                                                             0.005                                                                            --   0.005                                                                            1.03                                                                             5.0  40 55  5 50 50 --                       32 1.01                                                                             --  0.01                                                                              0.01                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.04                                                                             3.0  25 60 15 30 -- 70                       33 1.01                                                                             0.01                                                                              --  0.01                                                                              0.03                                                                              --  0.03                                                                              1.05                                                                             7.0  25 60 15 70 30 --                       34 1.00                                                                              0.005                                                                            --   0.005                                                                            --   0.005                                                                             0.005                                                                            1.01                                                                             5.0  20 65 15 -- 20 80                       35 1.00                                                                             --   0.005                                                                             0.005                                                                            --   0.015                                                                             0.015                                                                            1.02                                                                             1.0  25 70  5 -- 50 50                       36 1.00                                                                             0.01                                                                              --  0.01                                                                               0.005                                                                             0.0005                                                                           0.01                                                                              1.02                                                                             0.0  -- -- -- -- -- --                       37 1.00                                                                             0.01                                                                              0.01                                                                              0.02                                                                              --  0.01                                                                              0.01                                                                              1.03                                                                             1.0  15 60 25 60 15 35                       38 1.00                                                                             --  0.01                                                                              0.01                                                                              0.02                                                                              0.01                                                                              0.03                                                                              1.04                                                                             1.0  25 55 20 50 35 15                       39 1.00                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.04                                                                             1.0  24 75  1 100                                                                              -- --                       40 0.99                                                                              0.005                                                                             0.005                                                                            0.01                                                                               0.005                                                                             0.005                                                                            0.01                                                                              1.01                                                                             1.0  30 50 20 40 45 15                       41 0.99                                                                             0.01                                                                              --  0.01                                                                              0.02                                                                              --  0.02                                                                              1.02                                                                             7.0  20 40 40 30 65  5                       42 0.99                                                                             --   0.002                                                                             0.002                                                                            --   0.028                                                                             0.028                                                                            1.02                                                                             1.0  15 55 30 60 20 20                       43 0.99                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.01                                                                              --  0.01                                                                              1.02                                                                             1.0  20 70 10 -- 70 30                       44 0.99                                                                             0.01                                                                              0.02                                                                              0.03                                                                              0.01                                                                              --  0.01                                                                              1.03                                                                             3.0  40 55  5 50 -- 50                       45 0.99                                                                             --   0.049                                                                             0.049                                                                            --   0.001                                                                             0.001                                                                            1.04                                                                             10.0 10 50 40 20 55 25                       46 0.99                                                                             --  0.02                                                                              0.02                                                                              --  0.03                                                                              0.03                                                                              1.04                                                                             3.0  15 70 15 80 -- 20                       47 0.98                                                                              0.002                                                                            --   0.002                                                                             0.018                                                                            --   0.018                                                                            1.0                                                                              0.2  39 60  1 -- 100                                                                              --                       48 0.98                                                                             --  0.02                                                                              0.02                                                                              --  0.01                                                                              0.01                                                                              1.01                                                                             3.0  10 55 35 100                                                                              -- --                       49 0.98                                                                             --  0.02                                                                              0.02                                                                              --  0.01                                                                              0.01                                                                              1.01                                                                             3.0  10 55 35 -- 100                                                                              --                       50 0.98                                                                             --  0.02                                                                              0.02                                                                              --  0.01                                                                              0.01                                                                              1.01                                                                             3.0  10 55 35 -- -- 100                      51 0.98                                                                             --  0.01                                                                              0.01                                                                              --  0.03                                                                              0.03                                                                              1.02                                                                             5.0  15 80  5 -- 50 50                       52 0.98                                                                             0.03                                                                              --  0.03                                                                              --  0.01                                                                              0.01                                                                              1.02                                                                             1.0  30 60 10 20 80 --                       53 0.98                                                                             0.02                                                                              --  0.02                                                                              0.03                                                                              --  0.03                                                                              1.03                                                                             1.0  30 65  5 50 -- 50                       54 0.97                                                                             --   0.002                                                                             0.002                                                                             0.028                                                                            --   0.028                                                                            1.0                                                                              0.2  49 50  1 -- 100                         55 0.97                                                                             0.01                                                                              --  0.01                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.0                                                                              12.0 35 60  5 50 50 --                       56 0.97                                                                             0.02                                                                              --  0.02                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.01                                                                             3.0  20 65 15 20 40 40                       57 0.97                                                                             0.03                                                                              --  0.03                                                                              0.01                                                                              --  0.01                                                                              1.01                                                                             12.0 10 65 25  5 90  5                       58 0.97                                                                             --   0.002                                                                             0.002                                                                             0.048                                                                            --   0.048                                                                            1.02                                                                             0.2  40 50 10  5 75 20                       59 0.97                                                                             --  0.01                                                                              0.01                                                                              --  0.04                                                                              0.04                                                                              1.02                                                                             1.0  15 65 20 20 20 60                       60 0.97                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.02                                                                              0.01                                                                              0.03                                                                              1.02                                                                             0.2  30 55 15  5  5 90                       61 0.97                                                                             --  0.03                                                                              0.03                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.02                                                                             5.0  45 40 15 20  5 75                       62 0.96                                                                             0.01                                                                              --  0.01                                                                              0.01                                                                              0.02                                                                              0.03                                                                              1.00                                                                             0.2  20 50 30  5 35 60                       63 0.06                                                                             --  0.03                                                                              0.03                                                                              --  0.01                                                                              0.01                                                                              1.00                                                                             3.0  -- 55 45 40 30 30                       64 0.96                                                                             0.01                                                                              --  0.01                                                                              0.04                                                                              --  0.04                                                                              1.01                                                                             3.0  20 55 25 30 20 50                       65 0.96                                                                             --  0.02                                                                              0.02                                                                              0.02                                                                              0.01                                                                              0.03                                                                              1.01                                                                             1.0  5  75 20 35 35 30                       66 0.95                                                                             --   0.002                                                                             0.002                                                                             0.028                                                                            --   0.028                                                                             0.098                                                                           10.0 30 55 15 45 20 35                       67 0.95                                                                              0.002                                                                            --   0.002                                                                            --   0.048                                                                             0.048                                                                            1.00                                                                             1.0  10 70 20 70 15 15                       68 0.95                                                                              0.049                                                                            --   0.049                                                                             0.001                                                                            --   0.001                                                                            1.00                                                                             0.2  29 70  1 -- -- 100                      69 0.95                                                                             0.03                                                                              --  0.03                                                                              0.01                                                                              0.01                                                                              0.02                                                                              1.00                                                                             --   -- -- -- -- -- --                       70 0.94                                                                             0.01                                                                              0.01                                                                              0.02                                                                              0.02                                                                              0.02                                                                              0.04                                                                              1.00                                                                             0.2  20 65 15 35 55 10                       71 0.93                                                                             0.02                                                                              --  0.02                                                                              0.01                                                                              0.01                                                                              0.02                                                                              0.98                                                                             2.0  10 60 30 25 40 35                       72  0.981                                                                            0.001                                                                            --   0.001                                                                            --  0.02                                                                              0.02                                                                              1.00                                                                             1.0  30 60 10 40 30 30                       __________________________________________________________________________

With use of the ceramic compositions of Table 3, we formulated testcapacitors of the same construction as those of Example I through thesame procedure as in Example I. Then we measured the four electricalproperties in question of the thus fabricated test capacitors by thesame methods as in Example I. The results were as given in Table 4. Wealso gave in this Table the maximum temperatures at which the moldedbodies of the respective compositions were fired in the nonoxidativeatmosphere. The atmosphere was, of course, reductive, consisting ofmolecular hydrogen and molecular nitrogen.

The average capacitance-temperature characteristic of the Test No. 29capacitors is represented more exactly in the graph of FIG. 3. Thecapacitors of Tests Nos. 30 through 72 exhibited a more or less similarcapacitance-temperature characteristic in the same temperature range.

                                      TABLE 4                                     __________________________________________________________________________    Firing Temperatures & Capacitor Characteristics                                      Capacitor Characteristics                                                 Firing                                                                            Specific                                                                            Dielectric                                                       Test                                                                             Temp.                                                                             Dielectric                                                                          Loss  Resistivity                                                                          Capacitance Variations (%)                          No.                                                                              (°C.)                                                                      Constant                                                                            (%)   (megohm-cm)                                                                          At -25° C.                                                                    At +85° C.                            __________________________________________________________________________    29 1070                                                                              2820  1.6   2.1 × 10.sup.6                                                                 -7.2   +4.8                                         30     Not coherently bonded on firing.                                       31 1090                                                                              2910  1.1   6.8 × 10.sup.6                                                                 -11.2  +10.6                                        32 1120                                                                              3020  0.9   6.5 × 10.sup.6                                                                 -9.2   +2.5                                         33 1070                                                                              Not coherently bonded on firing.                                       34 1110                                                                              2950  1.0   6.4 × 10.sup.6                                                                 -12.8  +11.6                                        35 1160                                                                              3100  1.2   4.2 × 10.sup.6                                                                 -8.7   +6.3                                         36 1250                                                                              Not coherently bonded on firing.                                       37 1160                                                                              3090  1.3   4.2 × 10.sup.6                                                                 -7.4   -2.6                                         38 1150                                                                              3020  1.2   3.8 × 10.sup.6                                                                 -7.2   -1.4                                         39 1160                                                                              2990  1.8   2.6 × 10.sup.6                                                                 -7.3   -1.2                                         40 1150                                                                              3050  1.3   3.5 × 10.sup.6                                                                 -9.1   +4.8                                         41 1250                                                                              2930  1.5   5.4 × 10.sup.6                                                                 -5.8   +2.1                                         42 1160                                                                              3150  1.3   3.4 × 10.sup.6                                                                 -6.2   +1.8                                         43 1160                                                                              3080  1.1   4.1 × 10.sup.6                                                                 -7.2   +2.3                                         44 1110                                                                              2870  1.2   6.3 × 10.sup.6                                                                 -6.8   -2.4                                         45 1070                                                                              2640  1.8   2.5 × 10.sup.6                                                                 -9.6   -9.1                                         46 1130                                                                              2840  0.8   6.7 × 10.sup.6                                                                 -9.5   -5.4                                         47 1170                                                                              3210  2.2   1.5 × 10.sup.6                                                                 -6.2   +4.8                                         48 1130                                                                              3000  0.9   6.9 × 10.sup.6                                                                 -7.2   -2.2                                         49 1130                                                                              2990  0.8   7.0 × 10.sup.6                                                                 -7.4   -3.2                                         50 1130                                                                              2980  0.9   6.9 × 10.sup.6                                                                 -7.0   -3.4                                         51 1250                                                                              Not coherently bonded on firing.                                       52 1150                                                                              2910  1.0   3.2 × 10.sup.6                                                                 -7.3   -6.4                                         53 1150                                                                              2820  1.4   2.8 × 10.sup.6                                                                 -9.4   -3.4                                         54 1170                                                                              3230  1.8   1.4 × 10.sup.6                                                                 -6.7   +4.5                                         55 1070                                                                              2740  2.3   5.7 × 10.sup.5                                                                 -7.1   -4.9                                         56 1130                                                                              2890  0.9   6.9 × 10.sup.6                                                                 -6.7   -3.8                                         57 1070                                                                              2610  2.6   6.8 × 10.sup.5                                                                 -9.5   -9.7                                         58 1170                                                                              3020  1.6   1.8 × 10.sup.6                                                                 -9.1   +0.7                                         59 1160                                                                              2950  1.2   3.5 × 10.sup.6                                                                 -9.2   -5.1                                         60 1180                                                                              3010  1.3   1.9 × 10.sup.6                                                                 -9.1   -6.3                                         61 1250                                                                              Not coherently bonded on firing.                                       62 1180                                                                              3170  1.2   2.0 × 10.sup.6                                                                 -8.3   -1.4                                         63 1250                                                                              Not coherently bonded on firing.                                       64 1120                                                                              2800  0.9   3.5 × 10.sup.6                                                                 -7.8   +1.2                                         65 1250                                                                              Not coherently bonded on firing.                                       66 1070                                                                              2740  7.8   2.6 × 10.sup.3                                                                 -8.3   -3.2                                         67 1160                                                                              2960  1.1   2.2 × 10.sup. 6                                                                -8.7   -4.3                                         68 1190                                                                              2870  1.7   2.0 × 10.sup.6                                                                 -9.1   -9.6                                         69 1250                                                                              Not coherently bonded on firing.                                       70 1190                                                                              2910  1.2   3.8 × 10.sup.6                                                                 -13.8  -8.7                                         71 1120                                                                              2930  8.9   3.2 × 10.sup.3                                                                 -7.3   -5.8                                         72 1140                                                                              3090  2.6   2.6 × 10.sup.6                                                                 -8.5   +7.5                                         __________________________________________________________________________

Prior to a detailed discussion of the results of Table 4, we will firstpoint out that the measured properties of Tests Nos. 30, 31, 33, 34, 36,41, 51, 55, 57, 61, 63, 65, 66, 69, 70, 71 and 72 do not meet the aboveestablished criteria of favorable capacitors. The corresponding ceramiccompositions of Table 3 fall, therefore, outside the scope of ourinvention.

The Test No. 36 composition contained no additive, and the resultingdielectric bodies were not coherently bonded on firing at a temperatureas high as 1250° C. However, when 0.2 part by weight of the additive(mixture of Li₂ O, SiO₂, BaO, CaO and SrO) was added to 100 parts byweight of the major ingredient, as in Test No. 60, the capacitors of thedesired electrical characteristics could be obtained by firing at alower temperature of 1180° C. The lower limit of the possibleproportions of the additive is thus set at 0.2 part by weight withrespect to 100 parts by weight of the major ingredient even when theadditive contains MO, just as when it does not. When as much as 12 partsby weight of the additive (mixture of Li₂ O, SiO₂, BaO, CaO, and SrO)was added to 100 parts by weight of the major ingredient, as in Test No.57, the resulting capacitors had the average dielectric loss of as muchas 2.6 percent. Capacitors of the desired characteristics could beobtained when the proportion of the additive was reduced to 10 parts byweight, as in Test No. 29. The upper limit of the possible proportionsof the additive (including MO) is, therefore, also 10 parts by weightwith respect to 100 parts by weight of the major ingredient, just as incases where the additive contains no MO.

As for the major ingredient, Ba_(K-x-y) M_(x) L_(y) O_(k) TiO₂, thevalue of x+y was set at 0.01 in Test No. 31. In the resultingcapacitors, the average variations of capacitances at -25 and +85 C. are-11.2 and +10.6 percent, both outside the desired range of plus or minus10 percent. However, when the value of x+y was increased to 0.02, as inTest No. 29, then the desired electrical characteristics could all beobtained. Thus the lowermost possible value of x+y is 0.02. The Test No.70 composition had the value of x+y set at as high as 0.06. In theresulting capacitors, the average variation of capacitance at -25° C. is-13.8 percent, which also is outside the desired range of plus or minus10 percent. In Test No. 46, the value of x+y was set slightly lower, at0.05, and the resulting capacitors possess all the desired electricalcharacteristics. The uppermost possible value of x+y is therefore 0.05.

The value of x was set at 0.001 in Test No. 72. The resulting capacitorshas an average dielectric loss of 2.6 percent, which exceeds the desiredlimit of not more than 2.5 percent. The value of x was set at 0.002 inTests Nos. 42 and 47, and the resulting capacitors had the desiredelectrical characteristics. The lowermost possible value of x istherefore 0.002.

Sr and Ca, represented by the capital L in the formula of the majoringredient, both function as aforesaid to expedite the sintering of theceramic bodies formulated in accordance with our invention. As will beseen from Tests Nos. 45 and 68, Sr and Ca both perform their intendedfunction when the value of y in the formula of the major ingredient isat least 0.001. The lowermost possible value of y is therefore 0.001,regardless of whether the additive of the ceramic compositions inaccordance with our invention contains MO or not.

Since we have set the maximum possible value of x+y at 0.05, and theminimum possible value of y at 0.001, it follows that the maximumpossible value of x is 0.049, as in Tests Nos. 45 and 68, just as incases where the additive contains no MO. Further, since we have set theminimum possible value of x at 0.002, the maximum possible value of y isnecessarily 0.048, as in Tests Nos. 58 and 67, just as in cases wherethe additive contains no MO. As will be seen from the results of Table4, x can be in the range of 0.002 to 0.049, y in the range of 0.001 to0.048, and x+y in the range of 0.02 to 0.05, regardless of whethereither or both of Mg and Zn are employed as M, and whether either orboth of Sr and Ca are employed as L.

The value of k in the formula of the major ingredient was set at 0.98 inTest No. 66, with the result that the average resistivity of theassociated capacitors is 2.6×10³ megohm-centimeters, much lower than therequired minimum. However, the desired criteria of resistivity and otherproperties were obtained when k was set at 1.00 as in Tests Nos. 47 and54. The lowermost possible value of k is therefore 1.00. On the otherhand, when the value of k was increased to 1.05, as in Test No. 30, theresulting dielectric bodies were not coherently bonded on firing. As inTest No. 32, however, the desired electrical characteristics resultedwhen the value of k was set at 1.04. Accordingly, the uppermost possiblevalue of k is 1.04, just as in cases where the additive contains no MO.

We have ascertained from the results of Table 4 that, when the additivemixture contains MO (one or more of Bao, Cao, and SrO), the acceptablerelative proportions of Li₂ O, SiO₂, and MO can be determined inaccordance with the indications of the ternary diagram of FIG. 4. Thepoint A in this diagram represents the Test No. 29 additive compositionof five mole percent Li₂ O, 70 mole percent SiO₂, and 25 mole percentMO. The point B indicates the Test No. 45 additive composition of 10mole percent Li₂ O, 50 mole percent SiO₂, and 40 mole percent MO. Thepoint C indicates the Test No. 54 additive composition of 49 molepercent Li₂ O, 50 mole percent SiO₂, and one mole percent MO. The pointD indicates the Test No. 39 additive composition of 24 mole percent Li₂O, 75 mole percent SiO₂, and one mole percent MO. The relativeproportions of the additive mixture of Li₂ O, SiO₂, and MO in accordancewith our invention all fall within the region bounded by the linessequentially connecting the above points A, B, C and D.

Table 4 proves that the additive compositions within this region makespossible the provision of capacitors of the desired electricalcharacteristics. The additive compositions of Tests Nos. 51, 61, 63, and65 are all outside that region, and the corresponding dielectric bodieswere not coherently bonded on firing. In the case of the Test No. 41additive composition, also outside the required range, the dielectricbodies were not coherently bonded on firing at temperatures less than1200° C. The above specified recommended range of the relativeproportions of the additive mixture holds true regardless of whetheronly one of BaO, CaO, and SrO is employed as MO, as in Tests Nos. 39,47, 48, 49, 50, and 54, or two or all of them are employed in suitableproportions as in the other Tests.

Although we have disclosed our invention in terms of specific Examplesthereof, we understand that our invention is not to be limited by theexact details of such disclosure but is susceptible to a variety ofmodifications within the usual knowledge of the ceramics or chemicalsspecialists without departing from the scope of the invention. Thefollowing, then, is a brief list of such possible modifications:

1. The low temperature sinterable ceramic compositions of our inventionmight include various additives not disclosed herein. An example is amineralizer such as manganese dioxide. Used in a proportion (preferablyfrom 0.05 to 0.10 percent by weight) not adversely affecting the desiredproperties of the inventive ceramic compositions, such a mineralizerwould improve their sinterability.

2. The start materials for the ceramic compositions of our inventionmight be substances other than those employed in the Examples herein,examples being oxides such as BaO and Li₂ O, hydroxides, etc.

3. The temperature of reheating in an oxidative atmosphere might bedetermined variously in consideration of such factors as the particularbase metal electrode material in use and the degree of oxidationrequired for the ceramic material.

4. The temperature of co-sintering in a nonoxidative atmosphere mightalso be changed in consideration of the particular electrode material inuse.

5. The low temperature sintered ceramic material of our invention mightbe used as the dielectric bodies of capacitors other than those of themultilayered type disclosed herein.

6. The atmosphere of sintering could be neutral.

What we claim is:
 1. A low temperature sintered ceramic materialconsisting of:100 parts by weight of Ba_(k-x-y) M_(x) L_(y) O_(k) TiO₂,where M is at least either of magnesium and zinc, L is at least eitherof strontium and calcium, k is a numeral in the range of 1.00 to 1.04, xis a numeral in the range of 0.002 to 0.049, y is a numeral in the rangeof 0.001 to 0.048, and x+y is a value in the range of 0.02 to 0.05; and0.2 to 10.0 parts by weight of an additive mixture of lithium oxide andsilicon dioxide the sintered ceramic material providing dielectrics forcapacitors having specific dielectric constants of over 2000, dielectriclosses of less than 2.5 percent, resistivity of over 1+10⁶megohm-centimeters, and temperature dependences of capacitances of plusor minus 10 percent in a temperature range -25° to +85° C.
 2. A lowtemperature sintered ceramic material as set forth in claim 1, whereinthe additive mixture consists of 25 to 50 mole percent lithium oxide and50 to 75 mole percent silicon dioxide.
 3. A low temperature sinteredceramic material consisting of:100 parts by weight of Ba_(k-x-y) M_(x)L_(y) O_(k) TiO₂, where M is as least either of magnesium and zinc, L isat least either of strontium and calcium, k is a numeral in the range of1.00 to 1.04, x is a numeral in the range of 0.02 to 0.049, y is anumeral in the range of 0.001 to 0.048, and x+y is a value in the rangeof 0.02 to 0.05; and 0.2 to 10.0 parts by weight of an additive mixtureof lithium oxide, silicon dioxide and at least one metal oxide selectedfrom the group consisting of barium oxide, calcium oxide, and strontiumoxide, the sintered ceramic material providing dielectrics forcapacitors having specific dielectric constants of over 2000, dielectriclosses of less than 2.5 percent, resistivity of over 1×10⁶megohm-centimeters, and temperature dependences of capacitances of plusor minus 10 percent in a temperature range of -25° to +85° C.
 4. A lowtemperature sintered ceramic material as set forth in claim 3, whereinthe range of the relative proportions of lithium oxide, silicon dioxide,and at least one selected metal oxide constituting the additive mixtureis in that region of the ternary diagram of FIG. 4 attached hereto whichis bounded by the lines sequentially connecting:the point A where theadditive mixture consists of five mole percent lithium oxide, 70 molepercent silicon dioxide, and 25 mole percent metal oxide: the point Bwhere the additive mixture consists of 10 mole percent lithium oxide, 50mole percent silicon dioxide, and 40 mole percent metal oxide; the pointC where the mixture consists of 49 mole percent lithium oxide, 50 molepercent silicon dioxide, and one mole percent metal oxide; and the pointD where the additive mixture consists of 24 mole percent lithium oxide,75 mole percent silicon dioxide, and one mole percent metal oxide.